1. Field of Invention
The present invention relates to a suppression device and, in particular, to a transient current suppression device.
2. Related Art
The transient interval is the required time period for a circuit system to transit from a transient state to a stable state. During the transient interval, the voltage or current of the circuit system is called a transient voltage or a transient current. When the DC power voltage is connected to a capacitor, the capacitor is in a short circuit at this instant. At this moment, the capacitor has no internal resistance or very small internal resistance, so that it is very possible to generate a larger transient current. If the transient current is conducted to a ground end and the ground end is connected the ground end of the power circuit, the system state of the power circuit can be easily affected. Moreover, the electronic components inside the power circuit may be damaged.
In order to reduce the effect of the transient current, a transient current suppression device is discloses. FIG. 1 is a schematic diagram showing a conventional transient current suppression device 1. As shown in FIG. 1, the transient current suppression device 1 includes a filtering circuit 11, a delayed turn-on circuit 12 and a control circuit 13. The filtering circuit 11 includes a capacitor C and a diode D, and the delayed turn-on circuit 12 includes a first resistor R1, a first capacitor C1, and a first transistor Q1.
During the circumstance of the first time of switching power or the load hot-plug, the filtering circuit 11 receives a first power signal V1, and the first power signal V1 flows through the diode D and then charges the capacitor C. Meanwhile, the capacitor C is in short circuit, and a first current signal I1 is generated. The delayed turn-on circuit 12 receives a second power signal V2 and then charges the first capacitor C1 after a delayed time. After the charging procedure, the first capacitor C1 is discharged to turn on the first transistor Q1, thereby forming a first discharging path. Thus, the first current signal I1 can be conducted to the ground end through the first discharging path.
The transient current suppression device 1 can prevent the transient current, which is generated due to the first time of switching power, from flowing back to the power circuit. However, if the second time of switching power is occurred in a short time period or several times of switching power are continuously performed, because the first capacitor C1 still contains electricity, the first transistor Q1 can be turned on at the moment that the second time of switching power is performed. Consequently, the first current signal I1 is immediately flowing to the ground end and then flowing to the power circuit, which provides the first power signal V1 and the second power signal V2.
FIG. 2 is a schematic diagram showing the current waveform of the first current signal I1 of FIG. 1. Herein, the stable current is about 200 mA, and the peak of the transient current is about 720 mA, which is three to four times of the stable current. Accordingly, if the transient current flows back to the power circuit, the state of the power circuit can be affected, and moreover, the internal electronic components thereof may be damaged, which may cause the malfunction of the power circuit. If the power circuit is a user system, the undesired malfunction may shut down the entire system, which will result in a huge lost.
Therefore, it is an important subject of the invention to provide a transient current suppression device that has a simple circuit design for decreasing the transient current and can be applied to hot-plug or frequent switching in short period.